Trust and deceit in the animal kingdom

Liesbeth Sterck

Animal Ecology, UUEthology Research, BPRC

Trust

Nature in tooth and claw

• Monkey business• Sly as a fox

Cooperation in theory

• Evolution on level individual

• Altruism: benefit for

other, costs for individual

• Problem with cheaters

Cooperation in theory

• Mutualism: simultaneous exchange of benefits

• Altruism: donor incurs cost; recipient benefits– Kin selection– Reciprocal altruism

Kin selection (Hamilton 1964)

• Altruism when:

• C < r*B

• Costs < relatedness * Benefits

• C < r*B r=1/2

r=1/4

r=1/8

Kin selection (Hamilton 1964)

Kin selection (Hamilton 1964)

• C < r*B

Animals can be nice to kin

http://www.youtube.com/watch?v=o2B1AJ3ZaUA

Cooperation with non-kin?

Reciprocal altruism (Trivers 1971)

• ‘If you scratch my back, I’ll scratch yours’• Non-kin• Not simultaneous

Prisoners Dilemma

• Cooperate or cheat (defect)

Reciprocal altruism (Trivers 1971)

• ‘If you scratch my back, I’ll scratch yours’• Non-kin• Not simultaneous• Repeated encounters• Individual recognition,

e.g. in a group

Humans• Humans are a group-living species

– Family / kin– Friends / acquaintances / colleagues

-- Warfare

Groups are diverse

• Size– From 2 - 100 - 10.000s individuals

• Composition– Changing- fixed

• Recognition group members– Anonymous –categories – individuals

• Reproduction– One female (+ male) - everyone

Cooperation in practice 1

• Why do primates live in groups?

Group living: advantages

• Warning against predators (van Schaik 1989)

Group living: disadvantages

• Competition (Wrangham 1980; Sterck et al. 1997}

Males:– Matings

Females:– Food

Group living: advantages

• Infanticide avoidance (Sugiyama 1965; 1966; Hrdy 1977; Sterck et al. 1997)

Balance in costs and benefits

Protection against predators and infanticide

Competition

Primate peculiarity:groups containboth females and males

Cooperation in practice 2

• How do primates live in groups?

How primates live in groups

• How complex is living in a primate group

• Do they take benefit others into account

Methods

• From individual to group:

• Observations• Behavioural experiments

Methods

• From individual to group:

• Observations• Behavioural experiments

• Computer simulations

How primates live in groups

• How complex is living in a primate group– Dominance– Good relationships

Relationships in group(Massen, Sterck & de Vos 2010)

KinDominanceFriendship

niet verwant0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

familie0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 30 31 32 33 34 35

Sitti

ng to

geth

er

2920 Timon (20)

Bob (29)

Good relationships

Advantages

Advantages male – female relationships

Friendship and mating success (Massen, Sterck et al. 2012)

Gro

omin

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mal

es (s

ec/h

our)

Mating season

*

2006/07 2007/080

10

20

30

40

50

60

70

80

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wel parenniet paren

Mating

No mating

Friendship and paternity(Massen, Sterck et al. 2012)

alle vader0

1

2

3

4

5

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ity o

f mal

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ank)

males

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other malefather

Friendship• Do they know their friends?

Computer simulation of behaviour (Hemelrijk 1998, 2000; Evers, Sterck et al. 2011, 2012, 2014)

Computer simulation of behaviour (Evers, Sterck et al. MS)

Grooming= friendship

Dominance

Dom

inan

ce

Computer simulation of behaviour (Evers, Sterck et al. MS)

Grooming = friendship

Dominance

Dom

inan

ce

niet verwant0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

familie0

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0.4

0.6

0.8

1

1.2

1.4

1.6

Primate group living

• Compete and cooperate in group• Relationships

– Kinship– Dominance– Friendship = ‘trust’

• Friendships take time to build and last long

Primate cooperation in practice 2

• Do they take benefit others into account?

– Other-regarding preferences– Inequity aversion

• Yerkes 1930’s: http://www.youtube.com/watch?v=zrv91Pa3jgs

Cooperation: pro-social behaviour• Do primates bestow other a favor?

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)

35

• To kin• To high-ranking animals

(Masse

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Bestow

Withhold

Neutral

High rank Low rank 36

Cooperation: pro-social behaviour

Inequity Aversion

"Inequity exists for a person whenever his perceived job inputs and/or outcomes stand

psychologically in an obverse relation to what he perceives are the inputs and/or outcomes of

another" (Festinger 1957)

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Inequity Aversion

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• Negative inequity aversion– React to getting less than other

• Positive inequity aversion– React to getting more than other

Inequity Aversion (Brosnan & de Waal 2003)http://www.youtube.com/watch?v=-KSryJXDpZo

capuchin monkey refuses food

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Inequity Aversion (IA): critisism

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• Newer data: no IA

The task for macaques

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O,5 kg O,5 kg2,3 kg2,3 kg

1. No effort (provisioning) Equity

2. No effort (provisioning) Inequity

3. Small effort Equity

4. Small effort Inequity

5. Large effort Equity

6. Large effort Inequity

7. Large effort Reward & effort inequity

The Conditions

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Friedman test: n = 19, 2 = 15.84, df = 2, p = 0.001

Post-hoc Wilcoxon signed ranks tests:

Provisioning vs. 0,5 kg: n = 19, T+=62.5, pexact= 0.115Provisioning vs. 2,3 kg: n = 19, T+= 152, pexact< 0.0010,5kg vs. 2,3 kg: n = 19, T+= 117.5, pexact= 0.008

Proportion of acceptance/performanceof all equity conditions for all animals

Significant drop in performance (for low value reward) with increasing workload

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Wilcoxon signed ranks tests:

Provisioning: n = 12, T+= 21, pexact= 0.719Small Effort: n = 12, T+= 34, pexact= 0.023Large Effort (reward): n = 12, T+= 8.5, pexact= 0.211Large Effort (reward & effort): n = 12, T+= 15.5, pexact= 0.250

Proportion of acceptance/performanceof dominant subjects

Disadvantageous Inequity aversion in small effort test

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Wilcoxon signed ranks tests:

Provisioning: n = 9, T+= 3, pexact= 0.156Small Effort: n = 9, T+= 4, pexact= 0.219Large Effort (reward): n = 9, T+= 0, pexact= 0.008Large Effort (reward & effort): n = 9, T+= 4, pexact= 0.055

AIA: Proportion of acceptance/performance of subordinate partners

Performance for low value reward decreases when workload increases

At high workload, performance for high value reward significantly better then for low value reward --> no advantageous inequity aversion

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Nature in tooth and claw?

• Monkey business• Sly as a fox

Care and friendship

• C < r*B

Conclusion

• Deceit kept in limits: otherwise no cooperation• Competition and cooperation in group

– Dominance and friendship

• Trust and friendship crucial for cooperation

Thank you

Humans are smart and have large brains

Social Intelligence Hypothesis• Primates have relatively large brains• Both cooperation and competition in group• Several hypotheses

– Primates ‘smart’ through social complexity

• Socially complex = socially intelligent

Social intelligence

• Evidence in favour:• Group size and brain size are correlated in

primates, cetaceans and carnivores (Dunbar 1998)